1. Field of the Invention
The invention relates to ammunition cartridges such as shotgun shells and the like. More particularly, the invention relates to projectile wads for ammunition cartridges.
2. Description of Related Art
FIG. 1 depicts a typical ammunition cartridge 20, which includes: a tube 24, a basewad 26, a metal head 28, and a projectile wad 44. An example of such an ammunition cartridge 20 is the WINCHESTER XPERT® shotshell by Olin Corporation, East Alton, Ill. The tube 24 is typically formed of plastic and may be of a type known the Reifenhauser tube. At the aft end 30 of the ammunition cartridge 20, the basewad 26 is inserted in a tight fitting relation into the aft end of the tube 24. The cup-shaped metal head 28 surrounds an aft portion of the tube 24 and is crimped to the outwardly-flared aft end of the tube 24 and basewad 26 to mechanically secure the three together and form an annular rim 32, which is useful to assist in extraction of the ammunition cartridge 20 from a shotgun (not shown). A central aperture 34 in the metal head 28 is co-aligned with a pocket 36 in the basewad to accommodate a battery cup-type primer 38 in press fit relation. The basewad 26 has a forward surface 42 that defines a portion of a powder chamber for receiving a propellant charge 40. The projectile wad 44 has an aft surface 43 forming an over-powder cup (powder cup), which typically bounds most of the remainder of the powder chamber. In the ammunition cartridge 20 shown in FIG. 1, the aft rim 45 of the projectile wad 44 is close to contacting a forward rim 46 of the basewad 26. Thus, between the aft rim 45 and the forward rim 46, the powder chamber may be bounded by a cylindrical segment of the interior surface 47 of the tube 24.
In the design of ammunition cartridges, a number of advancements have been made to improve the sealing of combustion gases against infiltration between the basewad 26 and tube 24. For example, U.S. Pat. No. 6,164,209 to Best et al. (the '209 patent) discloses an ammunition cartridge including a projectile wad having an aft portion located at least partially concentrically within a skirt of the basewad so as to define a powder chamber for containing the propellant charge. Upon firing of the ammunition cartridge, the pressure increase produces a radially outward force on the powder cup, causing the powder cup to expand radially and bear against the basewad to maintain a seal against escape of propellant combustion gasses from the powder chamber. Also, the basewad expands radially to seal combustion gasses against infiltration between the basewad and tube.
While the ammunition cartridge design described in the '209 patent is successful in improving the sealing of combustion gasses, room for improvement exists. For example, the ammunition cartridge described in the '209 patent includes a long, thin tapered basewad skirt that is designed to accept the projectile wad powder cup within an open end (mouth). The basewad skirt tapers to a sharp edge at the lip. This sharp edge is delicate and susceptible to damage at numerous points in the manufacturing process and during handling and conveying. It is not uncommon for the lip of the basewad skirt to have several minor dings and dents that cause inward deformation of material. This creates locations for the square edge of the powder cup skirt to catch as it is inserted into the shell, causing the powder cup to tip and seat improperly at an angle. Improper alignment of the powder cup can result in low report on firing and, in extreme cases, a bulge is created in the ammunition cartridge sidewall large enough to prevent chambering in the shotgun. Accordingly, care is taken during the manufacturing process to avoid powder cup misalignment, and any ammunition cartridges having a misaligned powder cup are discarded, which increases the production cost of the ammunition cartridges.